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mcnemar's test
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2022-08-26
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MCNEMAR'S TEST
When the data are correlated in some
way, for example, when two diagnostic
tests are compared by applying them
both to the same people, and then
observing the diagnosis from each
test (positive or negative),
condition 3 for the Chi-square test is
violated.
If we arrange our data as follows,
then it is managable with a test known
as McNemar's test. McNemar's test
uses the Chi-square statistic, and
tests the hypothesis that the two
diagnostic tests are equivalent.
The same hypothesis can be tested by
a straight-forward calculation of a
binomial probability. The program
also does the binomial calculation.
Suppose that two diagnostic tests
are both applied to 75 men. The
results can be tallied as follows:
TEST 1
positive negative
! ! !
---------------------------
! ! !
positive ! 32 ! 10 ! 42
! ! !
TEST 2 ---------------------------
! ! !
negative ! 7 ! 26 ! 33
! ! !
---------------------------
! ! !
! 39 ! 36 ! 75
! ! !
When the tests do not agree, do they
do so in about the same way? That is,
do the cases when TEST 1 is positive
and TEST 2 is negative occur in equal
numbers to the cases when TEST 1 is
negative and TEST 2 is positive?
We see in the example above that
those numbers are 10 and 7,
respectively. Is that a large enough
difference to make the tests
different?
If you want to run LOADSTAR 2X2
\oad"fisher",8
STATISTICS now, press "\".
Al Vekovius
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